3 cyl 65hp Merc - teach me a few things...

[WCTori]

Hi guys,..... new to Merc engines, and have a 3 cyl. 65hp to revive. Don't have the serial number in front of me, but i think it's of the red engine case years. (mid 70's ??? )

Anyway, I only have the powerhead as it's part of a very rare PWC (prototype from 1976) The motor would not turn over and i assumed the worst, - locked, siezed, rusted solid, who knows...... i tore it down today and looks like it was just stuck from the gooey 2 stroke. The pistons were basically glued to the cylinder walls. Everything looks good and perfect from what i've seen so far. Will clean up nicely. Looks like i'll need to replace the upper crank bearing, as it feels rough.

Does that bearing just press off/on ?

How do the reeds work on this motor ? I've never been inside a Merc before, so this is all new to me.

I've got lots of experience with the 2 stroke 50/60 hp Suzuki motors, so looking forward to learning about this one.

Thanks for any advise you can offer.

 

[jimmbo]

Well it wouldn’t have been from the Days of Red trimmed Cowls, those ended in 1971. The first year of the 3 cylinder was 72, also the first year for Blue trimming on the cowl.
Is there a silver coloured disc on the power head? If so it would have Serial # which is needed if you ever have to order parts.
The Reeds work just like any other Reeds, these are just buried a little deeper in the engine. Makes for a slightly smaller crankcase, increasing crankcase compression slightly compared to reeds in a manifold
ss you have noticed there is no cylinder head to remove. That makes boring and honing a bit more tedious. It also makes installing the pistons a bit of a pain as special compressors are needed.

The induction system is kind of odd, it has 2 carburetors feeding 3 cylinders, not one of Merc’s better designs, but because of the Reed Design...

The Bearing will have to be pressed off and on

 

[WCTori]

Hey thanks Jimmbo, Okay,... blue trim motor it is. Thank you. I'll look tomorrow for the silver disc. I guess the pulses inside the engine operate the reeds, these are just crankcase mounted.

Good to know about the ring compressor tool. Didn't even think about that at this point..... in the past i've been able to get buy on all my engines (if i didn't have the proper compressor) by using a large hose clamp. What's the tool look like for this motor ?

Anything else i should be looking out for with this motor ? All the wiring on it is dry and cracking, i think that'll be the worst part of getting it back up and running. Wonder if there are harnesses still available.

 

[jimmbo]

They look like this


Harnesses are available from 3rd Party Suppliers.

 

[The Force power]

Hey thanks Jimmbo, Okay,... blue trim motor it is. Thank you. I'll look tomorrow for the silver disc. I guess the pulses inside the engine operate the reeds, these are just crankcase mounted.

Good to know about the ring compressor tool. Didn't even think about that at this point..... in the past i've been able to get buy on all my engines (if i didn't have the proper compressor) by using a large hose clamp. What's the tool look like for this motor ?

Anything else i should be looking out for with this motor ? All the wiring on it is dry and cracking, i think that'll be the worst part of getting it back up and running. Wonder if there are harnesses still available.

I've brought a few of those back to life, before you get into it; check the distributor these parts are hard to find & expensive!
sometime it's better to buy an additional motor for parts.

These motors were notorious for burning up the #1 Piston & top bearing
As far as the wiring goes, I always peeled back the insulation/wrap/tape to about an inch away from the main plug & replace all wires (color-coded) lots of free schematics avail. solder/shrink tube all wires. that way you have a brand new harness.

 

[The Force power]

Found some pics.

It tricky but possible to remove one piston only & hone the cylinder-walls without pulling them all & needing the compression tools.

BTW, I like your Idea of the hose clamp

 

[Fed]

It is possible to put one back together using various screwdrivers, paddle pop sticks & plastic probe things.

I had a couple of those motors & the things that gave me problems were the bottom crank bearings & seals (speedi sleeves) and corroded exhaust baffle plates letting water into the cylinders.

MTFBWY very impressive getting one piston out & honing, I wouldn't have believed it unless I saw it, well done.

 

[jimmbo]

Only pulling on one Piston out and machining that one cylinder... It's called Cobbling it together, not a good repair practice. Mickey Mouse Repair would be another name for it.
Grit and Shavings from the machining operations will contaminate the other two cylinders, and since the Pistons aren't coming out a proper cleaning isn't going to happen.

Unlikely a hose clamp will work as due to the curvature of the crankcase. Which is why Kiekhaefer came up with their compressors.

 

[racerone]

Agreed ----Not sure how you would pull one piston out and hone one of these !-----Show me a video.

 

[The Force power]

jimmbo & raceone,

I'm not saying that is was a professional repair but it was success full.
When I used the tool to "clean-up" the cylinder wall I covered the area & washed out the cylinder draining through the spark plug hole.
I replaced it with a piston out of an identical block (that had a blown piston)

Thinking back, I think the hardest part was getting the needle-bearings back in place on wrist-pin.
lucky for me; I followed an advice from one of you two not to use a magnet. (some other old post)

Why would a hose-clamp not work?? it's going around the piston and not over & around the crank?
Sorry, I can not provide video "proof" of my claim

 

[The Force power]

It is possible to put one back together using various screwdrivers, paddle pop sticks & plastic probe things.

I had a couple of those motors & the things that gave me problems were the bottom crank bearings & seals (speedi sleeves) and corroded exhaust baffle plates letting water into the cylinders.

MTFBWY very impressive getting one piston out & honing, I wouldn't have believed it unless I saw it, well done.

Thank you Fed,

your forgetting the bubble gum that was used to keep it all together. lol

 

[jimmbo]

Some Piston Ring compressors are just oversized hose clamps. That design will work when installing pistons from above, where the Deck is Flat. Installing from the crankcase side is a different story. There there is no deck for the ring compressor to butt up against, and the cylinder walls are still below where the clamp will be stopped, by the curve of the crankcase

 

[The Force power]

Some Piston Ring compressors are just oversized hose clamps. That design will work when installing pistons from above, where the Deck is Flat. Installing from the crankcase side is a different story. There there is no deck for the ring compressor to butt up against, and the cylinder walls are still below where the clamp will be stopped, by the curve of the crankcase

Duly noted :tape:

 

[WCTori]

just went out to my powerhead, don't see a serial number. Is it typically in a specific spot ?

 

[jimmbo]

Mercury has placed them on the top of the Block, and other times have placed them on side of the block with the intake transfer passages. The Disk is about the size of a Quarter. A missing Disc is often a Sign that the Engine may have been overheated, or is possibly Hot in a different manner of speaking ,

 

[WCTori]

Anyone have the ring compressor they'd be willing to rent me ? Happy to pay you a deposit, and shipping both ways.

Just don't want to buy a tool i know i'll never use again.

 

[The Force power]

Anyone have the ring compressor they'd be willing to rent me ? Happy to pay you a deposit, and shipping both ways.

Just don't want to buy a tool i know i'll never use again.

I looked for them back then without success, luckily I did not need them; you may not either.

 

[Fed]

It's 100% doable without using the ring compressors, all the conrods bolted up & lower the whole thing down addressing each ring as they go in. A bit fiddly but not too bad, I did it solo but an extra set of hands would probably help.

 

[WillyBWright]

I always set the full throttle timing two degrees less than spec on those. It has to do with the gas, mostly. Once it starts to lose octane over time, that's when #1 seems to fry. Retarding wide-open-throttle timing by two degrees can save your motor with no discernable loss of top-end speed.

 

[WillyBWright]

I always set full throttle timing two degrees less than spec on those. It has to do with the gas. It loses octane over time in boats that aren't used frequently, and that's what fries #1. Retarding wide-open-throttle timing by two degrees prevents that with no discernable loss of top speed.